There is no real connection.
Gravity is 9.8 m/s^2. Not 9.8 * 10^8!!! And the result is kg m^2/s^2 not m/s^2.
The result assumes a free fall at 1 g. I multiply it by g in order to accomplish that. (It's on earth, it can't really fall slower. If you want it to fall slower, the only thing it can do is fall, hit something and stop, then fall again - but that has 0 impact on the energy released! The energy released does not care if the building hit something and stopped momentarily in the processes.)
I know the result looks superficially like the units for gravitational acceleration but it's not, it's also multiplied by kg * m. i.e. I multiply gravity by mass and by how far it fell. The end result is the units for energy.
If you look up Joule http://en.wikipedia.org/wiki/Joule you'll see that it is defined that way.
There is a reason they push so hard to make sure you do the units correctly in Physics - you can gain a lot of insight into what you are calculating if you manipulate them properly.